1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, particularly, to a semiconductor device comprising a capacitor using a ferroelectric material and a method of manufacturing the same.
2. Description of the Related Art
In recent years, the field of application of an LSI (large scale integrated circuit) is being expanded greatly. Specifically, the LSI was applied mainly in the past to, for example, a supercomputer, an EWS (Engineering Workstations) and a personal computer. However, the LSI is being mainly applied nowadays to, for example, a mobile apparatus and a multi-media system. As a result, it is important nowadays to impart a nonvolatile function to the LSI, in addition to low power consumption and high-speed operation. Also, it is important to introduce a new material into the LSI in order to impart a higher performance and more multi-functions to the LSI.
For example, a ferroelectric memory (ferroelectric RAM) with non volatility using a ferroelectric film, such as a film of a perovskite material or a film of a bismuth layered material, as an dielectric film of a capacitor for storing information attracts great attention recently. The ferroelectric memory, which can be substituted for a flash memory, an SRAM (Static RAM), and a DRAM (Dynamic RAM) and which can be applied to a logic circuit embedded device, has high expectations as a next-generation memory. Also, since the ferroelectric memory can be operated at high speed without using a battery, the ferroelectric memory has come to be used in a non-contact card such as an RF-ID (Radio Frequency-Identification).
The materials used for preparing a ferroelectric memory include highly volatile elements or elements which are diffused in the manufacturing process, and these react with other materials. As a result, the manufacturing process is greatly affected by the materials used for preparing ferroelectric memories.
A PZT film, i.e., Pb(Zr, Ti)O3 film, is one of the most typical composite oxides used as a ferroelectric film. Lead (Pb) contained in the PZT film has a higher vapor pressure than that of other elements contained in the PZT film. Therefore, a method, in which an amorphous film is formed first at a low temperature, followed by applying a heat treatment at a high temperature to the amorphous film so as to convert the amorphous film into a crystalline film, is generally employed for forming a PZT film. For example, widely employed is a method, in which an amorphous PZT film is formed first at room temperature by employing, for example, a sputtering method, followed by applying an RTA (Rapid Thermal Annealing) treatment to the amorphous PZT film in the oxygen atmosphere so as to instantly crystallize the amorphous PZT film.
However, since it is difficult to control the Pb amount throughout the manufacturing process, it is very difficult to manufacture a semiconductor device with a high accurate repeatability at a high yield. It should also be noted that, in order to improve the reliability of the semiconductor device, an oxide such as IrO2, RuO2, SRO (SrRuO3), or LSCO ((La, Sr)CoO3) is used for forming the electrodes of the capacitor. What should be noted is that these elements contained in the electrode material are diffused into the PZT film and react with Pb in grain boundary, resulting in degradation of I-V characteristics and poor ferroelectric property.
Further, the amorphous PZT film was annealed in oxygen ambient in the case of conventional crystallization. Hence, the crystals of the PZT film were exhibited a columnar structure as described herein later, resulting in the high leakage current and deterioration of switching endurance.
The use of a PZT film is referred to in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-156473 and U.S. Pat. No. 6,287,637B1. Each of these publications teaches that a PZT film formed first is annealed in an Ar gas atmosphere, followed by further annealing the PZT film in an oxygen gas atmosphere. However, the structure of the PZT film after the annealing treatment is not considered in each of these publications. Generally, it was difficult to obtain a ferroelectric capacitor excellent in the leakage characteristics.
As described above, the leakage current was increased and the fatigue property was degraded in the conventional ferroelectric capacitor, which make it difficult to obtain a capacitor excellent in I-V characteristics and reliability. Generally, it is of high importance to develop a semiconductor device comprising a capacitor of excellent characteristics and reliability, and a method of manufacturing the semiconductor device.